This invention relates to the field of providing a binary indication of the position of a rotating shaft for a duration of shaft rotation. The invention particularly relates to rotating cam limit switches.
Rotating cam limit switches have long been known and used to control various operations associated with machinery employing a rotating shaft. Examples of rotating cam limit switches are described in printed publications including issued U.S. Pat. Nos. 3,839,925 (to Ficken et al.) and 3,792,627 (to Tarello). Another example of a rotating cam limit switch has been on sale for more than a year. The sold limit switch consists of a cam hub wheel, two cam wheel actuators, two adjusting wheel and two elastomeric ring actuators. Each wheel actuator may activate a switch for 180 degrees in a rotation by a positive fixed lobe extending partially around the wheel perimeter. The cam profile for activating the switch is developed by meshing the individual profiles of each wheel actuator and providing a positive dwell between 180 degrees and 356 degrees of rotation. The individual wheel actuator profiles may be meshed to provide a negative dwell between 4 degrees and 180 degrees of rotation. Dwells ranging from 4 degrees through 356 degrees of rotation are possible with a transition taking place at 180 degrees between positive and negative dwell. Switch activation will be affected by the transition since normally open switch contacts would become normally closed contacts or conversely, normally closed switch contact would become normally open contacts. Each wheel actuator is separately adjusted by an associated adjusting wheel with an eccentric hub. An elastomeric ring gear is fitted over the eccentric hub and the gear engages a hub gear having internal teeth on the cam hub wheel, and engages an actuator gear having internal teeth on the wheel actuator. There is a one tooth difference between the hub gear and the actuator gear. When the elastomeric ring gear is rotated, the wheel actuator rotates with respect to the hub wheel. A first adjustment, employing a special tool engaging the hub wheel, initiates the dwell (or position) and a second terminates the dwell in dependence on the first adjustment. As a result, position can not be independently set from dwell.